Vibrio cholerae, the etiologic agent of cholera, is found naturally in environmental aquatic habitats both as a free-living organism and in a biofilm state attached to different surfaces, including mucilaginous surfaces of phytoplankton, chitinous surfaces of zooplankton and abiotic surfaces. It has been proposed that this facultative human pathogen uses biofilm formation and phenotypic variation as survival strategies which may be related to pathogenicity (Yildiz, F. H., and G. K. Schoolnik. 1999, Proc. Natl. Acad. Sci. USA 96:4028-4033). Biofilms are surface-attached microbial communities composed of microorganisms and the extra-polymeric substances they produce. After initial attachment, colonization of a surface is mediated by the movement and growth of attached bacteria, followed by the formation of microcolonies, which are often surrounded by extra-polymeric substances. Further growth of bacteria and continued production of exopolysaccharides (EPS) lead to the development of mature biofilms characterized by pillars and mushroom-like structures. In V. cholerae, the mannose-sensitive hemagglutinin type IV pilus (MSHA) and flagellum facilitate attachment to abiotic surfaces, and Vibrio, polysaccharide (VPS), which is part of the extracellular matrix, is required for the development of mature biofilms (Yildiz and G Schoolnik 1999, Proc. Natl. Acad. Sci. USA 96:4028-4033). Cells in the mature biofilms can return back to planktonic stage through detachment, thus completing the cycle. Polysaccharide lyases have been reported to be involved in biofilm detachment and cell dispersal in several biofilm-forming microorganisms.
V. cholerae, can undergo phenotypic variation in response to environmental stresses, resulting in rugose and smooth colonial variants (White 1938, J. Pathol. 46:1-6;, Yildiz and Schoolnik 1999 Proc. Natl. Acad. Sci. USA 96:4028-4033). Compared to the smooth variant, the rugose variant forms corrugated colonies, well-developed biofilms and exhibits increased levels of resistance to osmotic and oxidative stresses. Most of these rugose-associated phenotypes are due in part to increased production of VPS, which is mediated by proteins encoded by the vps genes [vpsA-K, VC0917-27, (vpsI cluster); vpsL-Q, VC0934-9, (vpsII cluster)] (FIG. 1). Mutations in any of the vps genes yield smooth colonial morphology and reduced capacity to form biofilms (Yildiz et al, 1999). The vps genes are organized into vpsI (11.5, kb) and vpsII (6.6, kb) coding regions on the large chromosome, separated by an 8.3, kb intergenic region (FIG. 1).